Background
Trudie Elizabeth James, resident of 53 Lonsdale Drive, Enfield, challenged a planning permission (ref: 25/03926/HOU) granted on 5 February 2026 by the London Borough of Enfield to construct part single/part two-storey side and rear extensions, a front porch, and loft conversion at the adjacent property, 51 Lonsdale Drive. James’s primary concern was the loss of daylight to a kitchen window (W1) in her home.
A Sunlight and Daylight Assessment submitted by the applicant used the Building Research Establishment (BRE) Guide methodology and calculated that while window W1’s Vertical Sky Component (VSC) would decline from 18.1% to 7.22%—retaining only 40% of its existing value and falling below BRE guidelines—the weighted average VSC across all windows serving the kitchen/conservatory space would increase to 101% of previous value, suggesting overall compliance. The council’s planning officer approved the permission based partly on this weighted average analysis and on permitted development rights as a fall-back position.
The claimant objected on grounds of mistake of fact, irrationality, failure to comply with the Public Sector Equality Duty (PSED) regarding a disabled resident’s health needs, and unlawful consideration of permitted development rights. She sought permission to apply for judicial review and interim relief (injunction and stay of the permission).
The Court’s Holding
The court heard argument on whether to grant permission for judicial review and whether to grant interim relief. The claimant contended that the council’s weighted average calculation was methodologically flawed under BRE guidance (para. 2.2.8) for two reasons: (1) the conservatory windows were not part of the same open-plan room as W1, and (2) at least some conservatory windows exceeded the 5-metre separation threshold beyond which weighted averaging is inappropriate. A post-permission BRE report commissioned by the claimant supported this critique, noting that the initial assessment had assumed a single open-plan space when the actual layout involved separate areas connected only by apertures.
The council argued that even if the kitchen/dining area was not technically open-plan, daylight reached the area through two additional apertures (a window and sliding doors leading to conservatories), and both conservatories received ample, unaffected light from the proposed development. The planning officer had reasoned that W1, although experiencing significant VSC loss, was not the primary light source for the room; the predominantly glazed rear elevation (windows W2–W24) contributed dominant daylight, none of which would suffer material loss. The officer applied the BRE weighted-average method to conclude the room as a whole would receive adequate daylight overall.
The judgment examines the legal standards for mistake of fact (established fact, uncontentious, objectively verifiable, material to the decision), irrationality (Wednesbury unreasonableness, high threshold), and PSED compliance (rigorous consideration of impacts on persons with protected characteristics before and at the time of decision). The court rehearses that fall-back developments relying on permitted development rights must show a realistic prospect of exercise, not mere possibility.
Key Takeaways
- Weighted-average daylight assessments under BRE guidance (para. 2.2.8) are appropriate only when windows light the same area of a room and are within 5 metres of each other; use in multi-room layouts with separated areas may be methodologically unsound.
- A planning officer’s failure to verify room layout information from available public records (prior planning permissions) before applying a technical assessment methodology may constitute a material mistake of fact.
- Permitted development rights may only be cited as a fall-back justification if there is evidence of realistic prospect of exercise, not mere theoretical availability.
- The PSED requires rigorous consideration of potential impacts on persons with protected characteristics (including disability) before the decision is made; mere acknowledgment in a template paragraph (“all equalities considerations duly considered”) may not satisfy the duty.
- In reviewing planning decisions by local authorities (as opposed to inspectors), courts apply the same Wednesbury unreasonableness standard; scope for reasonable disagreement on planning judgment is broad.
Why It Matters
This decision addresses tension between technical guidance (BRE) and planning judgment. The BRE Guide is not mandatory policy but widely used; councils must apply its methodology correctly when they invoke it. A weighted-average daylight calculation that pools dissimilar spaces can distort assessment outcomes and mask material impacts on individual windows, particularly where conservatories are treated as part of a single room when they are physically and legally separate. The judgment underscores that procedural unfairness and mistake of fact can arise from failure to consult the planning file itself when technical evidence depends on property layout.
The case also reinforces that the PSED is not a box-ticking exercise but requires substantive, rigorous consideration of how a decision affects persons with protected characteristics. Where an objector raises health or disability concerns linked to environmental impacts, the planning authority must grapple with those issues in real terms, not merely record that equalities duties have been “duly considered.” The outcome may inform future challenges to permissions granted with insufficient regard to health or equality impacts.